1. Field of the Invention
The present invention relates to an ink composition, a recording medium, an ink jet recording method, and printed matter, and more particularly relates to an ink composition, a recording medium, an ink jet recording method with which the optical stability (light resistance) of the printed matter is excellent, there is no ink clogging, the yellowing resistance of the printed matter is excellent, and a high-quality image can be obtained.
2. Description of the Related Art
Ink jet recording is a printing method in which tiny drops of an ink composition are ejected and made to adhere to a recording medium such as paper. A feature of this method is that images of high quality and resolution can be printed at high speed with a relatively inexpensive apparatus.
Various ink compositions have been proposed in the past for use in recording by this ink jet recording method.
There has been increasing need in recent years for better weatherproofness (particularly light resistance) of recorded images, and to this end there have been attempts at adding light stabilizers such as hindered amine compounds to ink compositions.
For instance, Dyes and Pigments 19 (1992, pp. 235-247) discusses that the photodegradation of a dye can be prevented by adding 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl (a hindered amine-based light stabilizer) to an aqueous solution containing this dye. Japanese Laid-Open Patent Application H11-170686, which was published in a later issue of the above journal (Dyes and Pigments 19) discloses a technique for stabilizing a water-soluble dye by adding a specific compound (the above-mentioned 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl or a derivative thereof) to a water-based ink jet recording liquid containing this water-soluble dye. This compound serves to halt the progress of a photo-oxidation reaction of a colorant and thereby prevent photodegradation by trapping radicals such as R• (alkyl radicals) produced by the optical excitation of carbonyl compounds and the like, or ROO• (peroxide radicals) produced by a reaction between R• and the oxygen in the air. Printed matter produced by ink jet recording using this recording liquid has outstanding light resistance.
However, while the light resistance of a recorded image is indeed improved by using an ink composition that contains the above-mentioned light stabilizer, a new problem is encountered in that if the printed matter is stored in a file equipped with a film containing an antioxidant composed of a specific phenol derivative, or if such a film is applied to the printed matter, the printed matter will yellow due to the effect of the light stabilizer.
The reason for this is believed to be that the specific phenol derivative reacts through the action of the hindered amine compound or other such light stabilizer contained in the ink composition fixed to the recording medium. BHT (2,6-di-tert-butyl-4-methylphenol) is an example of this specific phenol derivative.
Specifically, the above-mentioned phenol derivative contained in the film is sublimable and therefore migrates from the film to the printed matter, the action of the light stabilizer in the printed matter brings about the dimerization and quinonization of the phenol derivative, and the resulting reaction product is the cause of the yellowing of the printed matter. It is believed that this reaction is particularly pronounced and yellowing especially apt to occur when the light stabilizer has oxy radicals.
Even if the compound used as the light stabilizer does not have any oxy radicals, an oxidation reaction in the course of the printed matter being stored in the air can generate oxy radicals in the compound serving as the light stabilizer, so the yellowing reaction still proceeds, albeit more slowly, and the printed matter still ends up yellowing.